Device and method for inspecting an object

ABSTRACT

A device and method for inspecting an object ( 2 ) uses a bright field illumination beam path ( 4 ) of a bright field light source ( 5 ), said beam path being formed so that it passes through the projection optics ( 3 ), and a dark field illumination beam path ( 6 ) of a dark field light source ( 7 ), this beam path being formed so that it also passes through the projection optics ( 3 ). The object ( 2 ) can be projected by the projection optics ( 3 ) onto the least one detector ( 8 ), and the object ( 2 ) is simultaneously illuminated by both light sources ( 5, 7 ). In order to simultaneously detect bright field images and dark field images without involving complicated filtering operations, the light used for the dark field illumination is pulsed and the pulse intensity of the light used for the dark field illumination is greater by at least one order of magnitude than the intensity of the continuous light, which is used for the bright field illumination, during a pulsed interval.

The present invention relates to a device and a method for inspecting anobject, having a bright field illumination beam path of a bright fieldlight source formed with respect to an imaging optical arrangement,having a dark field illumination beam path of a dark field light sourceformed with respect to the imaging optical arrangement, the object beingimaged onto at least one detector by means of the imaging opticalarrangement and the object being illuminated simultaneously by the twolight sources.

Apparatuses of the generic type have been known for some time. Inoptical inspection technology, in particular, complex structures onplanar substrates are inspected image field by image field. This is thecase primarily in the semiconductor industry for optically examiningpatterned surfaces of masks and wafers. In this case, defects that arepresent, by way of example, are intended to be detected or classified.Examples of defects that occur may be grains of dust, blisters in theresist, resist residues on wafers, chipping of edges or scratches.

A microscope with Köhler bright field illumination, by way of example,may serve as the device. Thus, a bright field illumination is formed bythe Köhler illumination with regard to the microscope objective—that isto say the imaging optical arrangement and, if appropriate, theeffective detector area. A dark field illumination can be realized in aknown manner in the case of a microscope, for example by using a darkfield microscope objective. In the case of such an objective, the lightserving for the dark field illumination is guided between the imagingoptical arrangement for the bright field imaging and an objectivehousing formed in mirrored fashion in such a way that it impinges on theobject in an angular range or aperture range that lies outside thenumerical aperture of the imaging optical arrangement for the brightfield imaging. In order to define the bright field or dark fieldillumination beam path, it is necessary, if appropriate, to take accountof the effective detection area of the detector or the entire detectionbeam path running between object and detector, in particular when theaperture ranges of the bright field and dark field illumination beampaths virtually adjoin one another.

Experience shows that detection of elevated and recessed structures bymeans of bright field illumination alone is not possible or is possibleonly to a limited extent. For this reason, a transition has been made tocarrying out an additional inspection, which is effected with the aid ofa dark field illumination provided in the device. This type ofillumination is particularly suitable for the detection of elevated andrecessed structures, which structures may be defective structures.Planar structures remain invisible in the case of dark fieldillumination. In contradistinction, elevated structures appear with highcontrast as bright lines on a dark background. Irregularities in theselines indicate possible defects.

DE 199 03 486 A1 discloses a method for simultaneous bright field anddark field illumination in the case of which at least one of the twobeam bundles is encoded by means of the color—i.e. the wavelength of thelight—, the polarization or the modulation, i.e. amplitude or frequencymodulation. The bright field image is separated from the dark fieldimage by means of corresponding filters or detector devices.

Furthermore, DT 2 021 784, DE 23 31 750 C3 and DE 37 14 830 A1 discloseillumination devices for microscopes in the case of which a changeovercan optionally be made between bright field and dark field illumination.Simultaneous bright field/dark field illumination is not provided inthis case.

EP 0 183 946 B1 discloses combined bright field and dark fieldillumination with two light sources in the case of which a changeover ismade from bright field to dark field illumination by means of mechanicalclosures (shutters) that are respectively assigned to a light source. Inthis case, it is also provided that both types of illumination are usedsimultaneously, that is to say both shutters are opened. In this mode,however, the radiation of the bright field image surpasses that of thedark field image, so that simultaneous detection of an object with bothillumination modes is not possible.

Consequently, the illumination systems disclosed in the prior art areeither not suitable for simultaneous bright field and dark fieldillumination, or a simultaneous illumination in both modes is indeedpossible, but the images thus obtained are unusable or can only beseparated from one another with increased complexity.

Therefore, the present invention is based on the object of specifyingand developing a device and a method for inspecting an object in such away that a simultaneous detection of bright field and dark field imagesis possible, the intention being to dispense with complex filteroperations.

The device according to the invention for inspecting an object achievesthe above object by means of the features of patent claim 1.Accordingly, such a device is characterized in that the light servingfor dark field illumination is pulsed, and in that the pulse intensityof the light serving for dark field illumination is at least one orderof magnitude greater than the intensity—relative to a pulse interval—ofthe continuous light serving for bright field illumination.

According to the invention, it has firstly been recognized that theluminous efficiency differs greatly in the case of a bright fieldillumination and a dark field illumination. Thus, almost exclusively thelight reflected at the object is detected in the case of a bright fieldillumination, whereas almost exclusively the light scattered at theobject is detected in the case of a dark field illumination.Consequently, the intensity ratios differ greatly in the case of asimultaneous detection, for example 100:1 or 1000:1. Therefore, in themanner according to the invention, the pulse intensity of the lightserving for dark field illumination is chosen to be at least one orderof magnitude greater than the intensity—relative to a pulse interval—ofthe continuous light serving for bright field illumination, to beprecise relative to the intensity ratios of the light of the two lightsources at the object or in the object plane of the imaging system. As aresult of this, in a particularly advantageous manner, the intensity ofthe light scattered at the object by the dark field illumination iscomparable with or at least of the same order of magnitude as theintensity of the light reflected at the object by the bright fieldillumination, so that it is not necessary to make elevated requirementsof the properties—e.g. the dynamic range—of one or more detectors.

In a further manner according to the invention, the light serving fordark field illumination is pulsed. Consequently, strictly speaking, asimultaneous illumination by the two light sources is afforded only whenthe pulsed light of the dark field light source illuminates the object.This means, however, in an especially advantageous manner, that it isnot necessary to provide shutters in the illumination beam paths sinceeither only a bright field illumination or a simultaneous bright fieldand dark field illumination is present, as it were continuously. In thisrespect, object image data can be detected continuously by means of thedetector or by means of a detector system having a detector, in whichcase, in accordance with the temporal sequence of the illuminationconditions, only bright field images of the object and bright fieldimages together with dark field images of the object can be detected andevaluated. In principle, the pulse repetition frequency of the darkfield light source can be adapted to the read-out characteristic of thedetector.

The dark field light source used may be a light source whose light powerto be provided, relative to continuous operation, does not have to be 10or 1000 times as high as that of the continuously operated light sourcefor bright field illumination. The light power to be provided by thedark field light source relates to the power of the individual pulses.According to the invention, this light power is to be chosen to be atleast one order of magnitude greater than the intensity—relative to apulse interval—of the continuous light serving for bright fieldillumination. It is only by virtue of this high intensity of the darkfield light pulses that the dark field image of the object, withsimultaneous bright field illumination, can be detected withoutadditional filters or similarly separating detection devices, but ratherdirectly from the recorded image. In contradistinction thereto, thepreviously known devices always required additional filters,demodulation means, etc. in order to separate the dark field image fromthe bright field image. Suitable light sources that can be used as darkfield light sources are advantageously commercially available in a largeselection and in some instances inexpensively. Thus, by way of example,it is possible to use a Xenon flash lamp, a laser or an LED as darkfield light sources.

In concrete terms, the pulse intensity of the light serving for darkfield illumination is 10 to 10 000 times greater than theintensity—relative to a pulse interval—of the continuous light servingfor bright field illumination. Since, in particular, the intensity ofthe light scattered at the object depends on the object property or onthe property of the object surface, the intensity ratio of the two lightsources can be chosen in a manner dependent on the object to beinspected, in particular on the type of objects to be inspected, e.g.for masks for the semiconductor industry. Ultimately, the intensity ofthe continuously operating bright field light source for bright fieldillumination will be chosen in such a way that an optimum contrast canbe obtained with the detector or with the detector system in this case.The intensity of the pulsed dark field light source is then chosen insuch a way that an optimum contrast can likewise be obtained in the caseof the dark field illumination, and that both the image data detected inthe different illumination modes have an optimum intensity ratiorelative to one another.

In one possible embodiment of the device, the dark field light sourceemits pulsed light. What is involved in this case is a light source thatonly operates in pulsed operation. As an alternative, it may also beprovided that the dark field light source emits continuous light, orthat a partial beam of the bright field light source for the brightfield illumination is coupled out for the dark field illumination beampath. The continuous light is then subdivided into individual pulses bymeans of at least one optical component. This optical component may be ashutter, a rotating shutter wheel, an electro-optical or anacoustic-optical modulator, the optical component being arranged in thedark field illumination beam path.

In an especially preferred embodiment, the read-out and/or evaluationreadiness of the detector and/or of the detection system is synchronizedwith the pulse sequence of the light serving for dark fieldillumination. This measure makes it possible, on the one hand, to adaptthe properties of the detector and/or of the detection system to theillumination conditions currently prevailing, so that, in anadvantageous manner, an overdriving of the detector, by way of example,can be prevented to a greater extent. On the other hand, this measureenables the image data of the respective illumination mode to beassigned to the individual illumination modes with the aid of thedetection system and/or an evaluation system connected downstream of thedetection system, so that a targeted evaluation of image data can beeffected which takes account of the respective characteristics of thedetected images.

In concrete terms, the synchronization may be effected on the basis of apulse sequence signal of the dark field light source or on the basis ofa control signal of the optical component. If the pulsed dark fieldlight source has a trigger output that outputs a corresponding triggersignal if a light pulse is emitted, this signal can be utilized forsynchronization of the detector or the detection system. As analternative to this, it would be possible, by way of example, to effectsynchronization by detection of the pulse sequence of the dark fieldlight source on the basis of a partial beam which is extracted from thedark field light source and is conducted onto a photodiode. The outputsignal of said photodiode can then be used for synchronization. If acontinuously operating light source is used as the dark field lightsource, and this light is subdivided into individual pulses by means ofan optical component, then the control signal of the optical componentmay serve as synchronization signal for the detector and/or for thedetection system. Furthermore, a delay circuit that can be used tocompensate for electronic propagation time differences or temporaloffsets, by way of example, may be provided for synchronizationpurposes.

In a preferred embodiment, the optical axis of the bright fieldillumination beam path is essentially perpendicular to the surface ofthe object to be inspected or is essentially perpendicular to the objectplane of the imaging optical arrangement. This condition is met in thecase of an inspection system designed in the form of a microscope, byway of example, by virtue of the microscope having a Köhler illuminationsystem, since, in this case, the optical axis of the bright fieldillumination beam path is essentially perpendicular to the object planeof the imaging optical arrangement. If the inspection system is to beused to inspect objects with essentially planar surface structures—thusfor example wafers or masks for the semiconductor industry—, the objectto be inspected will expediently be oriented and/or positioned in such away that its surface is arranged perpendicular to the optical axis ofthe bright field illumination beam path. In the inspection of at leastpartly transparent masks for the semiconductor industry, a bright fieldillumination in the transmitted light mode is also conceivable, theoptical axis of the bright field illumination beam path then likewisebeing essentially perpendicular to the surface of the object to beinspected.

In another embodiment, the optical axis of a detection beam path runningbetween object and detector is essentially perpendicular to the surfaceof the object to be inspected. In this respect, an arrangement of thedetection beam path as is present in a conventional microscope, by wayof example, may be involved in this case. The bright field illuminationbeam path may thus overlap or run coaxially with the detection beam pathin regions.

The optical axis of the dark field illumination beam path may bearranged, at least in regions, coaxially with the optical axis of thebright field illumination beam path and/or coaxially with the opticalaxis of the detection beam path. This is the case in particular when adark field objective is used in the case of an inspection apparatusdesigned as a microscope, in which case the illumination beam paths ofthe two light sources may be arranged in a similar manner to that knownfor example from EP 0 183 946 B1.

In a preferred embodiment, the optical axis of the dark fieldillumination beam path has an angle of between 5 and 90 degrees withrespect to the optical axis of the bright field illumination beam pathand/or with respect to the optical axis of the detection beam path. Whatis involved in this case is, by way of example, an arrangement as knownfrom FIG. 5 from DE 199 03 486 A1, the dark field illumination beam paththus being led past the microscope objective on the object side, as itwere. In this case, in an especially advantageous manner, the anglebetween the optical axis of the dark field illumination beam path andthe optical axis of the bright field illumination beam path may be setin such a way as to obtain optimum results in the detection of theimages which are recorded by means of the dark field illumination.Consequently, the angle setting may have to be varied in a mannerdependent on the object structures to be detected. This can be achievedfor example by means of the optical components of the dark fieldillumination beam path; if appropriate, it is also possible to vary theillumination aperture of the dark field illumination and thus to effecta further adaptation to the object structures to be detected.

In principle, it is conceivable for the light of the bright field lightsource and/or of the dark field light source to have a coding. In thiscase, the technology disclosed in DE 199 03 486 A1 is combined with thedevice according to the invention. As a result of this, advantages maybe afforded, under certain circumstances, in the image data evaluationif, by way of example, the pulsed light of the dark field light sourcehas a wavelength of 488 nm, the light of the bright field light sourcehas a wavelength of 365 nm and the detector comprises a color CCDcamera. The detected image data can then be assigned to the respectiveillumination mode during the data evaluation solely with regard to thecolor information. Quite generally, the coding may be formed by thepolarization, amplitude modulation, frequency modulation, pulsefrequency modulation and/or by the selection of a wavelength or awavelength range.

The bright field light source used may be a white light source,preferably a DC lamp. Xenon, mercury-vapor high-pressure lamps or otherarc lamps in DC operation are usually used for inspection devices forinspecting wafers and masks for the semiconductor industry,corresponding color filters or reflection filters being able to filterout all wavelengths apart from a wavelength of the emission spectrum ofthe light source, which is then used for the object illumination. Lasersor LEDs (Light-Emitting Diode) that emit continuous light are likewiseconceivable.

The dark field light source may be designed as a Xenon flash lamp, alaser or an LED or LED arrangement, the dark field light source emittingpulsed light. The pulse durations of the pulses of the dark field lightsource to be used usually lie in a range of 1 ms to 0.01 ms, but arepreferably 0.1 ms. The pulse power of the individual pulses is typicallyof the order of magnitude of 1 watt in this case.

In a preferred embodiment, the detector comprises a CCD camera, it beingpossible to use a monochrome and/or a color CCD camera. The spatialresolution is generally higher in the case of a monochrome CCD camerathan in the case of a color CCD camera. A monochrome CCD camera ispreferably used particularly in the case of inspection devices and inthe case of coordinate measuring devices for inspecting or measuringcoordinates of wafers and masks in the semiconductor industry, where ahigh spatial resolution is demanded. The CCD camera control, inparticular, can be synchronized with the pulse sequence signal of thedark field light source with regard to the detection or read-outbehavior of the CCD camera.

In principle, the device according to the invention is coupled to acontrol computer. Usually, said control computer not only controlsautomatic image data recording of a plurality of objects that are to beinspected automatically, but also has a storage unit on which thedetected object data or extracted measurement results are stored and/orevaluated.

In respect of the method, the object mentioned in the introduction isachieved by means of the features of the coordinate patent claim 17.Accordingly, in the method for inspecting an object, the object isilluminated simultaneously with a bright field light source for brightfield illumination, on the one hand, and with a dark field light sourcefor dark field illumination, on the other hand, and the object is imagedonto at least one detector by means of an imaging optical arrangement.The method according to the invention for inspecting an object ischaracterized in that the light serving for dark field illumination ispulsed, the pulse intensity of the light serving for dark fieldillumination being at least one order of magnitude greater than theintensity—relative to a pulse interval—of the continuous light servingfor bright field illumination.

The method according to the invention is preferably used for operating adevice according to one of patent claims 1 to 16. In order to avoidrepetition, reference is made in this regard to the preceding part ofthe description.

It is especially preferred for the object inspection to be effectedautomatically. Thus, a program according to which differentpredetermined regions of the object are detected may be executed on acontrol computer assigned to the device. For this purpose, the devicemay be coupled to a positioning system that positions the objectrelative to the imaging optical arrangement and is preferably likewisedriven by the control computer. It is furthermore conceivable for aplurality of objects to be automatically fed to the device—for exampleby means of a loading robot—and to be detected fully automaticallyobject by object in each case in regions. The control computer mayfurthermore comprise a program module which makes it possible toevaluate the detected image data with regard to possible defects of therespective object. Methods of digital image processing may generally beused in this case, it being possible to provide a comparison of thedetected object regions with a known calibration object. Fordocumentation or logging of the defects identified, the correspondingimage regions of the respective object or merely their coordinates maybe stored on the storage unit of the control computer.

There are now various possibilities for configuring and developing theteaching of the present invention in an advantageous manner. In thisrespect, reference should be made, on the one hand, to the patent claimsthat are subordinate to patent claims 1 and 17 and, on the other hand,to the following explanation of the preferred exemplary embodiments ofthe invention with reference to the drawing. Generally preferredconfigurations and developments of the teaching are also explained inconjunction with the explanation of the preferred exemplary embodimentsof the invention with reference to the drawing, in which:

FIG. 1 shows a schematic illustration of a first exemplary embodiment ofa device according to the invention,

FIG. 2 shows a schematic illustration of a second exemplary embodimentof a device according to the invention,

FIG. 3 a shows a schematic illustration of a diagram of the temporalprofile of the light intensities of the illumination light of the brightfield light source and of the dark field light source at the location ofthe object in the case of the exemplary embodiment from FIG. 2,

FIG. 3 b shows a schematic illustration of a diagram of the temporalprofile of the light intensities of the light of the bright field lightsource and of the dark field light source, which light is reflected andscattered at the object, at the location of the detector in the case ofthe exemplary embodiment from FIG. 2,

FIG. 3 c shows a schematic illustration of a diagram of the temporalprofile of the light intensities of the light of the bright field lightsource and of the dark field light source, which light is reflected andscattered at the object, at the location of the detector in the case ofthe exemplary embodiment from FIG. 2, a different object having beingdetected, and

FIG. 4 shows a schematic illustration of a diagram of a temporal profileof a light pulse of the dark field light source and a detection intervalof the detector.

FIGS. 1 and 2 show schematic illustrations of a device 1 for inspectingan object 2. Said device 1 is an optical inspection device by means ofwhich masks and wafers for the semiconductor industry can be examined inparticular for defects. The device 1 has a bright field illuminationbeam path 4 of a bright field light source 5 formed with respect to animaging optical arrangement 3. Furthermore, a dark field illuminationbeam path 6 of a dark field light source 7 is provided with respect tothe imaging optical arrangement 3. The object 2 is imaged into adetector 8 by means of the imaging optical arrangement 3, the detectionbeam path 9 running from the object 2 to the detector 8. The object 2 isilluminated simultaneously by the two light sources 5 and 7.

According to the invention, the light of the dark field light source 7serving for dark field illumination is pulsed. FIG. 3 a shows aschematic diagram of the logarithm of the light intensities of the twolight sources 5 and 7 (lg I) in arbitrary units as a function of time t.In this case, the temporal intensity profile relates to the illuminationintensity profile of the light of the two light sources 5 and 7 that ispresent at the object 2. For the sake of simplicity, the temporalintensity profile 10 of only one light pulse of the dark field lightsource 7 is shown. The temporal intensity profile of the bright fieldlight source 5 is shown by means of the reference symbol 11. The brightfield light source 5 emits continuous light having a constant intensity.The diagram of FIG. 3 a shows that the pulse intensity I1 of the lightserving for dark field illumination is approximately two orders ofmagnitude greater than the intensity I2—relative to the pulseinterval—of the continuous light serving for bright field illumination.Consequently, the pulse intensity I1 of the light serving for dark fieldillumination, in this exemplary embodiment, is approximately 100 timesgreater than the intensity I2—relative to a pulse interval—of thecontinuous light serving for bright field illumination. This has theadvantage that the dark field image can be separated from the brightfield image without additional auxiliary means, such as e.g. filters,since it appears brighter than the bright field image itself directly onthe detector 8.

The temporal intensity profiles shown in FIGS. 3 b and 3 c correspond tothe light intensity—present at the detector 8—of the light of the brightfield light source 5 reflected at the object 2, on the one hand, and ofthe light of the dark field light source 7 scattered at the object 2, onthe other hand. The diagrams of the FIGS. 3 b and 3 c thus show thelight intensities of the light of the two light sources 5 and 7, whichlight is reflected and scattered at the object, in arbitrary units as afunction of time t. In the case of the temporal intensity profile shownin FIG. 3 c, the detection is based on a different object than was thecase for the detected temporal intensity profile from FIG. 3 b. It canbe gathered from FIGS. 3 b and 3 c that the two objects differ withregard to the intensity of the proportion of scattered light at theobject surfaces.

The dark field light source 7 shown in FIG. 2 is an arc lamp that emitspulsed light. The dark field light source 7 shown in FIG. 1 is likewisean arc lamp, but one which emits continuous light having a constantintensity. The light of the dark field light source 7 from FIG. 1 issubdivided into individual pulses after collimation by means of a lens12 with the aid of an optical component 13 designed in the form of arotating shutter wheel. The shutter wheel rotates about the rotationaxis 14 and has light-transmissive regions arranged circumferentiallythrough which the light of the dark field light source 7 can pass. A forexample circular region is masked out by the diaphragm 15, so that onlyan annular illumination cross section is present in the further courseof the dark field illumination beam path 6.

The read-out and evaluation readiness of the detector 8 and of thedetection system 16 arranged downstream of the detector 8 issynchronized with the pulse sequence of the light of the dark fieldlight source 7 serving for dark field illumination. In FIG. 1, thesynchronization line 17 connects the optical component 13 to thedetection system 16. In FIG. 2, the synchronization line 17 connects thedark field light source 7 from FIG. 2 to the detection system 16. Forsynchronization purposes, a trigger signal is made available in eachcase by the optical component 13 from FIG. 1 and the dark field lightsource 7 from FIG. 2. The trigger signal of the optical component 13 maybe generated by means of a light barrier (not depicted) by way ofexample. The dark field light source 7 from FIG. 2 generates a triggersignal on the basis of its internal control. The detector 8 is connectedto the detection system 16 arranged downstream by means of the controland read-out line 32. For synchronization purposes, a delay circuit 18is additionally provided whose offset or delay value can be altered inan adjustable manner.

FIG. 4 shows a schematic diagram of the temporal intensity profile 10 ofa light pulse which has a half value width of less than 0.1 ms indicatedby the two arrows. The time interval 19 extending from t1 to t3′identifies the duration in which the detector 8 is in read-out readinessfor the light of the dark field light source 7 scattered at the object.In this case, the instant t2 ideally lies centrally between the startand end values t1 and t3 of the time window 19, the instant t2identifying the center of the light pulse.

The geometrical arrangement of the optical beam paths is discussedbelow. The bright field illumination beam path 4 in FIGS. 1 and 2 runsfrom the bright field light source 5 via the beam splitter 20 to theobject 2. At the beam splitter 20, the light of the bright field lightsource 5 is reflected for the most part in the direction of the imagingoptical arrangement 3.

The dark field illumination beam path 6 in FIG. 1 runs from the darkfield light source 7 firstly to the beam splitter 21, at which the lightof the dark field light source 7 is reflected in a mirrored region—shownby solid lines—in the direction of the imaging optical arrangement 3.The illustration shows merely schematically how the light of the darkfield light source 7 that is reflected at the beam splitter 21 is guidedcoaxially outside the bright field illumination beam path 4 in thedirection of the object 2, the depiction of a focusing opticalarrangement required for this purpose having been dispensed with for thesake of simplicity. The central region of the beam splitter 21 istransparent—depicted in dash-dotted fashion—, so that the light of thebright field light source 5 and the light that is scattered or reflectedat the object 2, in the bright field illumination beam path 4 or in thedetection beam path 9, can pass through the beam splitter 21 in saidregion.

The dark field illumination beam path 6 in FIG. 2 runs from the darkfield light source 7 to the object 2, to be precise firstly via thecoupling-in optical arrangement 22, which couples the light of the darkfield light source 7 into the optical waveguide 23. The light emergingfrom the optical waveguide 23 is focused by means of the focusingoptical arrangement 24 into the focal region of the imaging opticalarrangement 3 onto the object 2.

It can be gathered from FIGS. 1 and 2 that the optical axis 25 of thebright field illumination beam path 4 between beam splitter 20 andobject 2 is perpendicular to the surface 26 of the object 2 to beinspected. At the same time, the optical axis 25 of the bright fieldillumination beam path 4 is arranged perpendicular to the object planeof the imaging optical arrangement 3, which coincides with the surface26 of the object 2 facing the imaging optical arrangement 3 and istherefore not depicted separately. The optical axis 27 of the detectionbeam path 9 running between object 2 and detector 8 is likewiseperpendicular to the surface 26 of the object 2 to be inspected andperpendicular to the object plane of the imaging optical arrangement 3.

The optical axis 28 of the dark field illumination beam path 6 in FIG.1, between beam splitter 21 and object 2, is coaxial with the opticalaxis 25 of the bright field illumination beam path 4 and coaxial withthe optical axis 27 of the detection beam path 9.

FIG. 2 shows that the optical axis 28 of the dark field illuminationbeam path 6 is at an angle 29—indicated by the arcuate double arrow—withrespect to the optical axis 25 of the bright field illumination beampath 4 and with respect to the optical axis 27 of the detection beampath 9.

The bright field light source 5 is a DC lamp. The detector 8 is a CCDcamera.

The detection system 16 also comprises a control computer—not depictedseparately—which drives the individual components of the device 1. Inparticular, the object inspection is carried out automatically by meansof a program executed on the control computer. For this purpose, thedetection system 16 of the device 1 is coupled via a line 31 to apositioning system 30, which is likewise driven by the control computerand positions the object 1. The positioning system 30 positions theobject 2 along the direction shown by the double arrow at thepositioning system 30 in FIGS. 1 and 2. Furthermore, an objectpositioning in the two opposite directions perpendicular thereto isprovided, that is to say out of the plane of the drawing of FIGS. 1 and2.

Finally, it should be pointed out that the exemplary embodimentsdiscussed above serve only for describing the claimed teaching, but donot restrict the latter to the exemplary embodiments.

LIST OF REFERENCE SYMBOLS

-   1 device-   2 object-   3 imaging optical arrangement-   4 bright field illuminating beam path-   5 bright field light source-   6 dark field illuminating light source-   7 dark field light source-   8 detector-   9 detection beam path-   10 temporal intensity profile of a light pulse from (7)-   11 temporal intensity profile of the light from (5)-   12 lens-   13 optical component, rotating shutter wheel-   14 rotation axis of (13)-   15 diaphram-   16 detection system-   17 synchronization line-   18 delay circuit-   19 time interval-   20 beam splitter-   21 beam splitter-   22 coupling-in optical arrangement-   23 optical waveguide-   24 focusing optical arrangement-   25 optical axis of (4)-   26 surface to be inspected of (2)-   27 optical axis of (9)-   28 optical axis of (6)-   29 angle between (27) and (28)-   30 positioning system-   31 line between (16) and (30)-   32 control and read-out line-   I1 pulse intensity of a light pulse from (7) at the location of the    object-   I2 intensity of the light from (5) at the location of the object-   t1 beginning of the time interval (19)-   t2 center of the light pulse-   t3 end of the time interval (19)

1. A device for inspecting an object, having a bright field illuminationbeam path of a bright field light source formed with respect to animaging optical arrangement, having a dark field illumination beam pathof a dark field light source formed with respect to the imaging opticalarrangement, the object being imaged onto at least one detector by meansof the imaging optical arrangement and the object being illuminatedsimultaneously by the two light sources characterized in that the lightserving for dark field illumination is pulsed, and in that the pulseintensity of the light serving for dark field illumination is at leastone order of magnitude greater than the intensity of continuous lightserving for bright field illumination; wherein the read-out and/orevaluation readiness of the detector and/or of a detection system issynchronized with the pulse sequence of the light serving for dark fieldillumination.
 2. The device as claimed in claim 1, characterized in thatthe pulse intensity of the light serving for dark field illumination is10 to 10 000 times greater than the intensity of the continuous lightserving for bright field illumination.
 3. The device as claimed in claim1, characterized in that the dark field light source emits pulsed light.4. The device as claimed in claim 1, characterized in that the darkfield light source emits continuous light that can be subdivided intoindividual pulses by means of at least one optical component.
 5. Thedevice as claimed in claim 4 characterized in that the optical componenthas a shutter, a rotating shutter wheel, an electro-optical or anacoustic-optical modulator.
 6. The device as claimed in claim 1,characterized in that a delay circuit is provided for synchronizationpurposes.
 7. The device as claimed in claim 1, characterized in that theoptical axis of the bright field illumination beam path is essentiallyperpendicular to the surface of the object to be inspected or isessentially perpendicular to the object plane of the imaging opticalarrangement.
 8. The device as claimed in claim 1, characterized in thatthe optical axis of a detection beam path running between the object anddetector is essentially perpendicular to the surface of the object to beinspected or is essentially perpendicular to the object plane of theimaging optical arrangement.
 9. The device as claimed in claim 1,characterized in that the optical axis of the dark field illuminationbeam path, at least in regions, is coaxial with the optical axis of thebright field illumination beam path and/or coaxial with the optical axisof a detection beam path.
 10. The device as claimed in claim 1,characterized in that the optical axis of the dark field illuminationbeam path has an angle of between 5 and 90 degrees with respect to theoptical axis of the bright field illumination beam path and/or withrespect to the optical axis of a detection beam path.
 11. The device asclaimed in claim 1, characterized in that the bright field light sourceis designed as a white light source.
 12. The device as claimed in claim1, characterized in that the dark field light source is designed as axenon flash lamp, a laser or an LED (Light Emitting Diode) or an LEDarrangement.
 13. The device as claimed in claim 1, characterized in thatthe detector is designed as a CCD camera.
 14. The device as claimed inclaim 1, further comprising a coupling to a control computer.
 15. Amethod for inspecting an object, the object being illuminatedsimultaneously with a bright field light source for bright fieldillumination, on the one hand, and with a dark field light source fordark field illumination, on the other hand, and the object being imagedonto at least one detector by means of an imaging optical arrangement,characterized in that the light serving for dark field illumination ispulsed, the pulse intensity of the light serving for dark fieldillumination being at least one order of magnitude greater than theintensity of continuous light serving for bright field illumination. 16.The method as claimed in claim 15, characterized in that the objectinspection is carried out automatically.
 17. The method as claimed inclaim 15, characterized in that a device is coupled to a positioningsystem that positions the object, and in that object regions selected bymeans of the positioning system are automatically positioned in theinspection position.